1. Technical Field
The present invention relates to a liquid ejection apparatus such as a printer.
2. Background Art
A liquid ejection apparatus such as a printer includes, for example, a liquid ejection head (which is, for example, a recording head) having nozzles through which liquid is ejected. The apparatus performs printing by ejecting the liquid through the nozzles. As methods of printing employed by a recording head, there are scanning methods and non-scanning methods. In the scanning method, a recording head performs printing by ejecting droplets while being moved. The non-scanning method involves use of an elongated line head or a multiple head. The line head includes nozzle rows defined in the entire range corresponding to the maximum printing width. The multiple head is formed by a plurality of recording heads in which nozzle rows are provided over the aforementioned range. In the non-scanning method, a recording medium is transported in printing while the recording heads are fixed.
If ejection of ink through a liquid ejection nozzle is suspended for an extended period of time, the ink may become viscous or fixed in the nozzle and thus clog the nozzle. To solve this problem, a printer may include a maintenance device that maintains a recoding head, as described in Japanese Patent No. 3155871 and Japanese Laid-Open Patent Publications Nos. 2003-154686, 11-91140, 11-115275, 2002-264350, 2002-210983, and 2004-330495.
The maintenance device includes a cap and a suction pump. The cap is capable of sealing a surface (hereinafter, referred to as a “nozzle forming surface”) of the recording head in which nozzle openings are defined by contacting the nozzle forming surface in such a manner as to encompass the nozzle openings. The suction pump performs suction through the cap when the cap seals the nozzle forming surface, or generates negative pressure in the space sealed by the cap. This causes suction cleaning (suction recovery) in which ink (liquid) is drawn from the nozzles. In this manner, viscous ink and bubbles of ink are removed from the nozzles and the nozzles are recovered to a state in which the nozzles are capable of effective ink ejection. Further, the maintenance device has a wiper that wipes the nozzle forming surface. After the suction cleaning is completed, the wiper wipes the nozzle forming surface to remove ink or paper particles from the nozzle forming surface. Such wiping also functions to maintain the forms of meniscuses (hereinafter, referred to as “nozzle meniscuses”) of ink in the nozzles. Variation of the forms of the nozzle meniscuses causes variation of the amounts of liquid ejection and thus the sizes of printing dots, which lowers printing quality. However, by maintaining the nozzle meniscuses through wiping, desirable printing quality is saved.
Japanese Patent No. 3155871 describes a device that performs suction cleaning on a recording head including a plurality of nozzle sets through which different types of ink is ejected. The device includes ink receiving means (a cap) and suction means. The ink receiving means selectively contacts and separates from a nozzle forming surface in which the nozzle sets are defined. The suction means draws ink from inside the ink receiving means. The ink receiving means has a plurality of ink receiving portions. While being held in contact with the nozzle forming surface of the recording head, the ink receiving portions define separate spaces. Each adjacent pair of the ink receiving portions are separated from each other by a single partition means (a partition rib), which selectively contacts and separates from the nozzle forming surface of the recording head. The suction means draws ink separately from the separate spaces defined in the ink receiving means and has switching means (a valve device), which switches the spaces subjected to suction from one to another. The valve device is formed by a cylinder, which is connected to a pump through a pump tube, and a piston. Two suction tube connection holes and a pump tube connection hole are defined in the cylinder. Tubes corresponding to a color ink ejection port cap portion and a black ink ejection port cap portion, which are defined in the cap by the rib, are connected to the suction tube connection holes. The pump tube, which is connected to a suction pump, is connected to the pump tube connection hole. When the piston reciprocates in an up-and-down direction through actuation of a motor or the like, an O ring slides on an inner wall surface of the cylinder. This changes the position of the O ring in such a manner as to switch the suction tube connection hole, to which the pump tube connection hole is connected, from one to the other. Japanese Patent No. 3155871 also discloses a pump having a valve including the above-described valve device and a pump that are formed integrally. If an ink tank is replaced and ink suction is carried out on the corresponding nozzle set of the recording head, the technique of this document prevents the ink suction from being performed on the nozzle sets other than the nozzle set corresponding to the replaced ink tank. This saves ink consumption and prevents mixture of the colors of the ink in the nozzles.
After such ink suction, idle suction is performed to collect the ink from inside the cap and the suction tube, which is connected to the cap, to a waste liquid tank. In such idle suction, the suction pump is actuated with the cap opened to the atmospheric air so as to prevent the ink from being drawn from the nozzles. For example, a maintenance mechanism disclosed in Japanese Laid-Open Patent Publication No. 2003-154686 includes an atmospheric air exposure valve and a suction pump. The atmospheric air exposure valve exposes the interior of the body of the cap to the atmospheric air. After completing ink suction, the maintenance mechanism performs idle suction by actuating the suction pump with the atmospheric air exposure valve maintained open. The atmospheric air exposure valve becomes open when the cap body is urged by the urging force of an urging member to project from a cap holder. The atmospheric air exposure valve is closed when the cap body is depressed by a predetermined amount against the urging force of the urging member. The cap holder is moved in an up-and-down direction as a movable pin for a cap, which drives the cap, is guided along a cam groove of a cylindrical cam through rotation of the cam. When the cap holder is located at an ink suction position, at which the cap holder is located closest to the nozzle forming surface, the cap body caps the nozzle forming surface with the atmospheric air exposure valve maintained closed. When the cap holder is arranged at an ink idle suction position, at which the cap holder is retreated from the ink suction position, the cap body caps the nozzle forming surface with the atmospheric air exposure valve maintained open.
Further, although suction cleaning is carried out usually as periodical cleaning that is repeatedly performed each time a constant time period elapses, defective ejection may be caused by a nozzle prematurely. Thus, it is desirable that a defective ejection nozzle be detected even before the periodical cleaning and cleaning be performed if a defective ejection nozzle is detected. As a device that detects such a defective ejection nozzle, a device using a laser beam described in Japanese Laid-Open Patent Publication No. 2002-210983 and a device detecting reflected light of light radiated onto a printed pattern disclosed in Japanese Laid-Open Patent Publication No. 2004-330495 are known.
If a defective ejection nozzle is detected by the detection device described in Japanese Laid-Open Patent Publication No. 2002-210983 or Japanese Laid-Open Patent Publication No. 2004-330495, the nozzle row including the detected nozzle is selected and subjected to suction cleaning. This reduces the consumption amount of the ink wasted through cleaning, not through printing.
However, if operation of the device is selected between suction and non-suction, such selection must be carried out among suction, non-suction, and idle suction for each of the caps independently. It is thus necessary to arrange a suction passage valve in each of the passages connected to the caps. An atmospheric air exposure valve also must be provided for each of the caps. For a cap for which suction is not selected, it is desirable that an atmospheric air exposure passage be open when the cap contacts the nozzle forming surface, as described in Japanese Laid-Open Patent Publication No. 2003-154686. This prevents the meniscuses in the nozzles from being deformed by the pressure in the cap increased by an elastic portion of the cap deformed through contact with the nozzle forming surface. The atmospheric air exposure valve described in Japanese Laid-Open Patent Publication No. 11-91140 can be provided for the respective caps. However, in this case, cam mechanisms including cylindrical cams also must be arranged for the respective caps. This increases the size of an atmospheric air exposure valve mechanism. It is also necessary to provide a suction passage valve for the respective one of the caps separately from the corresponding atmospheric air exposure valve. In this case, a valve device disclosed in Japanese Patent No. 3155871 or Japanese Laid-Open Patent Publication No. 2003-154686 may be employed. However, the valve device of Japanese Patent No. 3155871 includes a cylinder and a piston and is relatively large. Thus, if this valve device is employed as a suction passage valve, the size of the valve unit is increased. This disadvantageously increases the size of the maintenance device and thus the size of the liquid ejection apparatus.
The three types of operations, which are suction, idle suction, and non-suction, are brought about by combining the open/closed states of the suction passage valve and the atmospheric air exposure valve. Specifically, to perform suction, the suction passage valve must be maintained open and the atmospheric air exposure valve must be maintained closed. To carry out idle suction, the suction passage valve and the atmospheric air exposure valve both must be maintained open. If non-suction is selected, the suction passage valve must be maintained closed and the atmospheric air exposure valve must be maintained open. Thus, as the valve unit mounted in the maintenance device that selectively performs suction in the above-described manner, it is necessary to provide a smaller-sized valve unit capable of operating the suction passage valve and the atmospheric air exposure valve in accordance with the three patterns of combinations of the open/closed states.